1. Field of the Invention
The present invention relates to multilayer capacitor greatly reducing the equivalent serial inductance (ESL), more particularly relates to a multilayer capacitor used as a decoupling capacitor.
2. Description of the Related Art
In recent years, while advances have been made in reducing the voltage of power sources used for supplying power to large-scale integrated circuits (LSI's) and other integrated circuits, the load current has increased.
Therefore, it has become extremely difficult to keep fluctuations in the power source voltage to within tolerances when faced with rapid changes in the load current. Therefore, a decoupling capacitor (for example two-terminal structure multilayer ceramic capacitor) is now being connected to a power source. At the time of transitory fluctuation in the load current, current is supplied from this multilayer ceramic capacitor to the LSI of the central processing unit (CPU) etc. to suppress fluctuation of the power source voltage.
Along with the increasingly higher operating frequencies of today's CPU's, however, the fluctuations in the load current have become faster and larger. The equivalent serial inductance (ESL) of the decoupling capacitor itself now has a great impact on fluctuations of the power source voltage.
That is, since the ESL is high in a conventional multilayer ceramic capacitor, fluctuation of the power source voltage V easily becomes greater in the same way as above along with fluctuations in the load current i.
That is because the fluctuations in voltage at the time of transition of the load current are approximated by the following equation 1 and therefore the level of the ESL is related to the magnitude of fluctuation of the power source voltage. Further, from equation 1, reduction in the ESL can be said to be linked with stabilization of the power source voltage.dV=ESL·di/dt  equation 1
where,
dV is transitory fluctuation of voltage (V),
i is the fluctuation of current (A), and
t is the time of fluctuation (sec).
As a multilayer capacitor wherein the ESL is reduced, a multilayer capacitor shown in Japanese Unexamined Patent Publication No. 2003-51423 is known. According to this multilayer capacitor, parasitic inductance can be reduced. As a result, the ESL can be reduced. However, it has been required to further reducing the ESL.
Further, as a multilayer capacitor wherein the ESL is reduced, a multi-terminal multilayer capacitor is known. In the multi-terminal multilayer capacitor, by increasing external terminal electrode, current flow varying in direction can be realized in an internal conductor layer. As a result, further reducing of the ESL becomes possible.
However, in the multi-terminal capacitor, there are problems that preparing a plurality of internal conductor layer patterns is necessary, and that increasing number of external terminals results in higher manufacturing cost.
A capacitor having two patterns of conductor layers: a conductor layer of an internal layer portion and a protection conductor layer sandwiching the internal layer portion in stacking direction is shown in Japanese Unexamined Utility Model Publication No. 5-66951. However, the effects of reducing the ESL cannot be obtained sufficiently because the protection conductor layer is used for improving moisture resistance of the capacitor, and further, terminal electrodes are formed only on two end faces of a dielectric body in Japanese Unexamined Utility Model Publication No. 5-66951.
An object of the present invention is to provide a multilayer capacitor able to greatly reduce the ESL with low manufacturing cost.